Radiation detector



June 3, 1952 BB. SCHNEIDEF 2,599,352

RADIATION DETECTOR Filed March 8, 1947 M R m M W i i a 2 INVENTOR. 55mm M/IV 5.8CH/VE/DEP ATTORNEY Patented June 3, 1952 P s m ss ATENT -OFFI CE- RADIATION DETECTDR Benjamin B. Schneider, Chicago,'Ill.,fassignor to Texaco Deve opment Corporation, New York,

N. Y., a corporation of Delaware- Applicatibn'Marbh '8, 1947g-SlialN0. 733324:

acmims. (entic 93) This-invention relates toradiation detectors, more particularly togamrna ray detectors of the counter or pulse-producing type. 'If-he principal object or" the invention is the provision of a detector of this type which will have considerably greater effective cathode area or surface and thus ahigher efficiency than the conventional Geiger- Muller counter. v ifts is well known, are conventional Geiger- 'Muller-counter consists of a metaltube usually .cylindricalin shape constituting the cathode and athin anode-wire disposed along the longitudinal axis -of -the cathode and insulated therefrom.

These electrodes are enclosed inan envelope, commonly aglass tube, containing a gasata pressureof a 'few centimeters of mercury. The anode wire is maintained usually ata positive potential with respect to the cathode, this potential being nearly but not quite high enough to-cause a discharge to take place. If a gamma ray strikes the cathode member an electron may be ejected from the cathode metal into the gas filling causing ionization of the gas and a discharge ofthe counter with a current flow of the order of afew microamperes. This causes alarge voltage drop acrossa resistance connected in series with the high voltage supply and the anode and'by suitable amplification a mechanical recorder or other device capable of registering the discharges'of' the counter may be actuated.

In the United States Letters Patent toHare and Herzog, No. 2,397,073, granted March 19, 1946, a gamma ray'counter is disclosed "whichlhas a considerably higher efficiency than the conventional Geiger -lvlulwr counter. The counter disclosed in that patent comprises essentially a p1u-= ralityoffthincathode plates arranged in a bank and disposed-in parallel separated relation.* Between each adjacentpair of plates and in parallel thereto is disposed a grid of aplurality of fine wires. The plates are connected" together electrically to form the cathode of the device and the wire grids may be connected together to form the anode or if desired, the grids may be provided with separate leads so that their output may be separately amplified. It isof course necessary to "carefuliy mount the cathode plates of the Hare- Herzog device so that they will bep'rop erly and rigidly spaced. Sincethe multiple plate cathode disclosed in the aforementioned patent contains "a much greater eiiective surface from which electrons "can 'be ejected than the conventional counter with its cylindrical cathode, assuming the volumes of the two counters are the same, a much "higher efficiency can be-obtained. The-device of the present invention also -providesa large-effective cathode surface while also permitting the entire cathode to be formed as a unitary rigid structure.

In accordance with one embodiment of the in- -ven tion the cathode a: the counter isrorm'eu or a tubular metallic member which'ina'y be cylindrical and from'the inner'su'rface-of "whichfa plurality of thin metallic fins onwings'proje'ct the cylinder. 'A fine'wireloomprisi'ng theano'de is stretched along the longitudinal axis andthe width of the'cathode fins" is suchthatfth'eir inner edges willbe parallel to and spaced equidistantly from the anode "wire. 7 When a high'potentialfis impressed across the cathode 'andthe "anode an electrical field will result between the anode and the inner edges or the cathode fins, this fild being -uniform throughout "the ilength 'Of'the counter.

In another embodiment of the" invention the cathode is formed or a metalliciltube which ma he rectangular incross-section' From the opposite wider inner surfaces of the tube aplurality other and through the.space betweenthe inner edges ofthese fins agrid of a pluralitybfparallel anode'wires is stretched. -Becau'se of thereotangular shape of the cathode in' thisrfibod'iinent several of the counter un'itsinay be'd'is'pose'd'adjacent each otherand' alargeeffective cathodesur- :face'can then'be provided ina' minimumorspace. Likewise, in the embodiment described in "the foregoing paragraph a plurality'of'the cylindrical units may be disposed inadjacentfparallel r'elation and all of the units rnounted within asi'rigle casing containing the'gas filling.

For a better 'understanding'of the invention, reference'may be hadto the accompanyingldraw ing'in which Figure l is a vertical'perspectiveView, partlyin sec'tion'of a' detector comprising one embodiment of the invention,

.tudinal axis of-themember 1 tan anodewire l 4 is disposed, this wire being connectedto-oneend of a resistance R. *As shown in Figure-1' the high indication of the discharges of the counter.

Extending radially inwardly from the inner surface of the cylinder I2 are a plurality of thin metallic fins or wings It. The inner edges of 3 these fins are parallel to and spaced equidistantly from the anode wire l4 and may be attached rigidly, by any suitable means, to the cylinder l2. When the high voltage is impressed across the electrodes an electrical field results between the anode wire 14 and the fins IS. The anode wire 14 is, of course, insulated from the cathode I2 and from the casing ID if the latter is metallic as by means of any suitable insulating bushings, not shown. The cylinder I2 and the fins It; may be formed of any suitable metal and it has been found that brass sheet having a thickness of about 16 mils is a suitable material for these elements. It has also been found that a tungsten wire about 3 mils in thickness provides a satisfactory anode. The casing 10 will be filled with a gas or a gaseous mixture, and a mixture of about 97% argon and 3% petroleum ether at a pressure of about 20 inches of mercury has proven satisfactory. Another gas mixture which has been found very satisfactory consists of about 97% argon and 3% anhydrous ammonia.

In the embodiment. illustrated in Figure 3 of the drawing the cathode of the detector is formed as a tubular element 18 which may be rectangular in cross-section. Projecting inwardly from opposite inner surfaces of the element [8 are a plurality of metallic fins 20, these fins extending toward each other in pairs and providing a central space also rectangular in shape. ing through the space between the inner edges of the fins 20 is a grid 22 formed of a plurality, eight in this instance, of anode wires 24, these wires being arranged parallel to each other and each wire being preferably disposed in the plane of and midway between an opposing pair of fins. The fins 20 may be secured rigidly to the inner surfaces of the cathode element [8 or they may be placed in slots 26 formed in spacer elements 28, one of which is illustrated in Figure 4. Each of these spacer elements 28 is formed of electrically insulating material and is provided along the two longer edges with a plurality of the slots 26 in which the cathode fins 20 fit snugly. More or less of the spacer elements may be used depending upon the length of the counter and, in assembling, the fins and the spacer elements may be assembled first and then pushed into the tubular element [8. With this type of construction it will of course be necessary for the fins 2!] to be connected together electrically and to the element I8. Each spacer element 28 is also provided with an elongated slot or opening 38 through which the anode wires 24 extend.

It is not necessary that the tubular member It be formed as rectangular in cross-section but when in the shape shown in Figure 3 several of these units may be arranged side by side or in any desired manner. When so arranged a large amount of effective cathode surface will be provided in a minimum of space. The detectors of both the embodiments shown in Figures 1 and 3 can be made of any desired length and it has been found that elongated detectors of this type are well suited to the radioactive logging of bore holes and wells.

It is believed that but little further description of the operation is necessary. A gamma ray in striking the cathode walls l2 or l8 or one of the fins I 6 or 20 may eject an electron into the gas filling to cause ionization of the gas and thus a discharge of the counter which can be registered Extendby measuring the voltage drop across the resistance R shown in Figure 1. By providing the fins l6 and 20, the effective cathode, area is materially increased while at the same time a good electrical field results between the anode wires and the inner edges of the fins.

Although no casing has been shown for the counter electrodes illustrated in Figure 3 it is understood that these electrodes will either be mounted within a properly shaped casing corresponding to H) of Figure 1, or that the ends of the tubular cathode element l8 will be closed and sealed so that the cathode tube I8 will itself serve as the casing.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A radiation detector comprising a metallic cylindrical cathode member, an anode wire extending along the longitudinal axis of said cathode member, means for impressing an electrical potential across said cathode member and said anode, a plurality of elongated metallic fins disposed parallel to and projecting radially inwardly toward said anode wire from the inner surface of said cathode member, said cathode member having an electrically closed conductive surface extending substantially the length of said fins, the inner edges of said fins being parallel to and spaced equidistantly from said anode wire so that the strength of the electrical field will be the same between the anode wire and the inner edge of each of said fins, and a housing for said members adapted to contain a gaseous filling.

2. A radiation detector comprising a sealed housing containing a gaseous filling, a thin metallic cylindrical member disposed Within said housing and forming a cathode member, a plurality of elongated, thin, metallic fins projecting radiallyinwardly in parallel relation from the inner surface of said cylindrical member, the inner edges of said fins defining an elongated space substantially round in cross section and extending longitudinally through said cathode member, said cathode member having an electrically closed conductive surface extending substantially the length of said fins, an anode wire extending along the longitudinal axis of said elongated space, and means for impressing an electrical potential across said cathode member and said anode wire, the strength of the electrical field resulting between the anode wire and the inner edge of said fins being uniform throughout the length of the cathode member.

BENJAMIN B. SCHNEIDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Dec. 1933, PES. 676-678. 

